Providing the stroboscope marks on the pulled-down rim of the turntable has proven to be particularly advantageous.
It is known to apply such marks in a printing process, whereby the rim of the plate is rolled on a printing roller. With such a method the possibilities of formation of the rim of the plate and the marks, respectively, are limited insofar as only a planar printing image or picture can be produced. Moreover as a result of the unavoidable diameter tolerances, the roll-off methods also do not permit an exact maintenance of the spacing of the divisions and edge-sharp marks, respectively.
It is further known to produce the turntable with use of a mold as a die casting part and simultaneously also to apply the stroboscope marks so as to project with respect to the rim of the plate. The necessary contrast in lightness between the marks and their intermediate spaces is achieved by coloring the plate and subsequently lightly cutting the projecting marks. Indeed by the plastic, prominent standing-out marks, which marks can be rectangular or round, the marks have a substantially better appearance; however because of the necessary form-ability of the turntable, properly narrow limits are set for the design possibilities, particularly if several rows of marks are to be provided for different rotational speeds or frequencies, as customarily is the situation. In these cases, for example, the rim of the plate can not even be approximately cylindrical.
A further disadvantage is that by means of the deformation (elevation impact or eccentricity) which is unavoidable during the production of the plate, when the turntable turns, an image of the marks results which wanders in the rhythm in the rotational speed. With rectangularly shaped marks this indeed can be made inconspicuous by lightly cutting the marks only on a part of their lengths. The recess depth with the light cutting must still be comparatively large because of radial eccentricity or impact of the plate caused during production, so that unsightly, sharp and differently or dissimilarly high, grater-like contours develop. Moreover such a turntable is comparatively expensive.
It is generally known to produce contours by stamping (as in coin production), which contours project with respect to a surface. Such a method, however, because of the necessary high pressure is not suited for the production of the stroboscopic marks of concern here.